Fuel for use in fuel cell system

ABSTRACT

A fuel for a fuel cell system comprises wherein said fuel has distillation properties, the initial boiling point (initial boiling point 0) in distillation of 24° C. or higher and 50° C. or lower, the 10 vol. % distillation temperature (T 10 ) of 35° C. or higher and 70° C. or lower, the 90 vol. % distillation temperature (T 90 ) of 100° C. or higher and 180° C. or lower, and the final boiling point in distillation of 130° C. or higher and 210° C. or lower. The fuel for a fuel cell system has a high power generation quantity per weight, a high power generation quantity per CO 2  emission, a low fuel consumption, a small evaporative gas (evapo-emission), small deterioration of a fuel cell system comprising such as a reforming catalyst, a water gas shift reaction catalyst, a carbon monoxide removal catalyst, fuel cell stacks and the like to maintain the initial performances for a long duration, good handling properties in view of storage stability and inflammability, and a low preheating heat quantity.

TECHNICAL FIELD

The present invention relates to a fuel to be used for a fuel cellsystem.

BACKGROUND ART

Recently, with increasing awareness of the critical situation of futureglobal environments, it has been highly expected to develop an energysupply system harmless to the global environments. Especially urgentlyrequired are to reduce CO₂ to prevent global warming and reduce harmfulemissions such as THC (unreacted hydrocarbons in an exhaust gas),NO_(X), PM (particulate matter in an exhaust gas: soot, unburned highboiling point and high molecular weight fuel and lubricating oil).Practical examples of such a system are an automotive power system toreplace a conventional Otto/Diesel engine and a power generation systemto replace thermal power generation.

Hence, a fuel cell, which has high energy efficiency and emits only H₂Oand CO₂, has been regarded as a most expectative system to response torespond to social requests. In order to achieve such a system, it isnecessary to develop not only the hardware but also the optimum fuel.

Conventionally, as a fuel for a fuel cell system, hydrogen, methanol,and hydrocarbons have been candidates.

As a fuel for a fuel cell system, hydrogen is advantageous in a pointthat it does not require a reformer, however, because of a gas phase ata normal temperature, it has difficulties in storage and loading in avehicle and special facilities are required for its supply. Further, therisk of inflammation is high and therefore, it has to be handledcarefully.

On the other hand, methanol is advantageous in a point that it isrelatively easy to reform, however power generation quantity per weightis low and owing to its toxicity, handling has to be careful. Further,it has a corrosive property, special facilities are required for itsstorage and supply.

Like this, a fuel to sufficiently utilize the performances of a fuelcell system has not yet been developed. Especially, as a fuel for a fuelcell system, the following are required: power generation quantity perweight is high; power generation quantity per CO₂ emission is high; afuel consumption is low in a fuel cell system as a whole; an evaporativegas (evapo-emission) is a little; deterioration of a fuel cell systemcomprising such as a reforming catalyst, a water gas shift reactioncatalyst, a carbon monoxide conversion catalyst, fuel cell stacks andthe like is scarce to keep the initial performances for a long duration;a starting time for the system is short; and storage stability andhandling easiness are excellent.

Incidentally, in a fuel cell system, it is required to keep a fuel and areforming catalyst at a proper temperature, the net power generationquantity of the entire fuel cell system is equivalent to the valuecalculated by subtracting the energy necessary for keeping thetemperature (the energy for keeping balance endothermic and exothermicreaction following the preheating energy) from the actual powergeneration quantity. Consequently, if the temperature for the reformingis lower, the energy for preheating is low and that is thereforeadvantageous and further the system starting time is advantageouslyshortened. In addition, it is also necessary that the energy forpreheating per fuel weight is low. If the preheating is insufficient,unreacted hydrocarbon (THC) in an exhaust gas increases and it resultsin not only decrease of the power generation quantity per weight butalso possibility of becoming causes of air pollution. To say conversely,when some kind of fuels are reformed by the same reformer and the sametemperature, it is more advantageous that THC in an exhaust gas is lowerand the conversion efficiency to hydrogen is higher.

The present invention, taking such situation into consideration, aims toprovide a fuel suitable for a fuel cell system satisfying theabove-described requirements in good balance.

DISCLOSURE OF THE INVENTION

Inventors of the present invention have extensively investigated tosolve the above-described problems and found that a fuel comprisinghydrocarbon compounds with specific distillation properties is suitablefor a fuel cell system.

That is, the fuel for a fuel cell system according to the presentinvention comprises:

(1) hydrocarbon compounds with distillation properties, the initialboiling point (initial boiling point 0) in distillation of 24° C. orhigher and 50° C. or lower, the 10 vol. % distillation temperature (T₁₀)of 35° C. or higher and 70° C. or lower, the 90 vol. % distillationtemperature (T₉₀) of 100° C. or higher and 180° C. or lower, and thefinal boiling point in distillation of 130° C. or higher and 210° C. orlower.

The fuel comprising hydrocarbon compounds with the above-describeddistillation properties is preferable to satisfy the followingadditional requirements;

(2) a content of hydrocarbon compounds having a carbon number of 4 is 15vol. % or less, a content of hydrocarbon compounds having a carbonnumber of 5 is 5 vol. % or more, a content of hydrocarbon compoundshaving a carbon number of 6 is 10 vol. % or more, a content ofhydrocarbon compounds having carbon numbers of 7 and 8 in total is 20vol. % or more, and a content of hydrocarbon compounds having carbonnumbers of 10 or more is 20 vol. % or less;

(3) a sulfur content is 50 ppm by mass or less;

(4) saturates are 30 vol. % or more;

(5) olefins are 35 vol. % or less;

(6) aromatics are 50 vol. % or less;

(7) a ratio of paraffins in saturates is 60 vol. % or more;

(8) a ratio of branched paraffins in paraffins is 30 vol. % or more;

(9) heat capacity of the fuel is 2.6 kJ/kg° C. or less at 15° C. and 1atm in liquid phase;

(10) heat of vaporization is 400 kJ/kg or less;

(11) Reid vapor pressure (RVP) is 10 kPa or more and less than 100 kPa;

(12) research octane number (RON, the octane number by research method)is 101.0 or less;

(13) oxidation stability is 240 minutes or longer; and

(14) density is 0.78 g/cm³ or less.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a flow chart of a steam reforming type fuel cell systememployed for evaluation of a fuel for a fuel cell system of theinvention.

FIG. 2 is a flow chart of a partial oxidation type fuel cell systememployed for evaluation of a fuel for a fuel cell system of theinvention.

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, the contents of the invention will be described further indetail.

In the present invention, the hydrocarbon with specific distillationproperties is as follows.

The fuel for a fuel cell system of the invention has initial boilingpoint (initial boiling point 0) in distillation of 24° C. or higher and50° C. or lower, preferably 27° C. or higher, and more preferably 30° C.or higher. The 10 vol. % distillation temperature (T₁₀) is 35° C. orhigher and 70° C. or lower, preferably 40° C. or higher, and morepreferably 45° C. or higher. The 90 vol. % distillation temperature(T₉₀) is 100° C. or higher and 180° C. or lower and preferably 170° C.or lower. The final boiling point in distillation is 130° C. or higherand 210° C. or lower and preferably 200° C. or lower.

If the initial boiling point (initial boiling point 0) in distillationis low, the fuel is highly inflammable and an evaporative gas (THC) iseasy to be generated and there is a problem to handle the fuel.Similarly regarding to the 10 vol. % distillation temperature (T₁₀), ifit is less than the above-described restricted value, the fuel is highlyinflammable and an evaporative gas (THC) is easy to be generated andthere is a problem to handle the fuel.

On the other hand, the upper limit values of the 90 vol. % distillationtemperature (T₉₀) and the final boiling point in distillation aredetermined in view of a high power generation quantity per weight, ahigh power generation quantity per CO₂ emission, a low fuel consumptionof a fuel cell system as a whole, a low THC in an exhaust gas, shortstarting time of a system, small deterioration of a reforming catalystto retain the initial properties, and the like.

Further, the 30 vol. % distillation temperature (T₃₀), 50 vol. %distillation temperature (T₅₀), and 70 vol. % distillation temperature(T₇₀) of the fuel of the invention are not particularly restricted,however, the 30 vol. % distillation temperature (T₃₀) is preferably 50°C. or higher and 100° C. or lower, the 50 vol. % distillationtemperature (T₅₀) is preferably 60° C. or higher and 120° C. or lower,and the 70 vol. % distillation temperature (T₇₀) is 80° C. or higher and150° C. or lower.

Incidentally, the above-described initial boiling point (initial boilingpoint 0) in distillation, the 10 vol. % distillation temperature (T₁₀),the 30 vol. % distillation temperature (T₃₀), the 50 vol. % distillationtemperature (T₅₀), the 70 vol. % distillation temperature (T₇₀), the 90vol. % distillation temperature (T₉₀), and the final boiling point indistillation are distillation properties measured by JIS K 2254,“Petroleum products-Determination of distillation characteristics”.

Further, the amounts of hydrocarbon compounds having carbon numbers of4, 5 and 6 of the invention are not particularly restricted, however,the following compounds are preferable.

The content of hydrocarbon compounds having a carbon number of 4 (V(C₄)) shows the content of hydrocarbon compounds having 4 carbon atomson the bases of the whole fuel and is required to be 15 vol. % or lesssince the evaporative gas (evapo-emission) can be suppressed to low andthe handling property is good in view of inflammability or the like andpreferably 10 vol. % or less and most preferably 5 vol. % or less.

The content of hydrocarbon compounds having a carbon number of 5 (V(C₅)) shows the content of hydrocarbon compounds having 5 carbon atomson the bases of the whole fuel and is required to be 5 vol. % or more inview of a high power generation quantity per weight, a high powergeneration quantity per CO₂ emission, and a low fuel consumption of afuel cell system as a whole and preferably 10 vol. % or more, morepreferably 15 vol. % or more, further more preferably 20 vol. % or more,much further more preferably 25 vol. % or more, and most preferably 30vol. % or more.

The content of hydrocarbon compounds having a carbon number of 6 (V(C₆)) shows the content of hydrocarbon compounds having 6 carbon atomson the bases of the whole fuel and is required to be 10 vol. % or morein view of a high power generation quantity and a low fuel consumptionof a fuel cell system as a whole and preferably 15 vol. % or more, morepreferably 20 vol. % or more, further more preferably 25 vol. % or more,and most preferably 30 vol. % or more.

The content of hydrocarbon compounds having carbon numbers of 7 and 8 (V(C₇+C₈)) in total shows the content of hydrocarbon compounds having 7carbon atoms and 8 carbon atoms in total on the bases of the whole fueland is required to be 20 vol. % or more in view of a high powergeneration quantity per weight, a high power generation quantity per CO₂emission, and a low fuel consumption of a fuel cell system as a wholeand preferably 25 vol. % or more, more preferably 35 vol. % or more, andmost preferably 40 vol. % or more.

Further, in the invention, the content of hydrocarbons having carbonnumbers of 10 or more is not particularly restricted, however, in viewof a high power generation quantity per CO₂ emission, a low fuelconsumption of a fuel cell system as a whole, and small deterioration ofa reforming catalyst to maintain initial performances for a longduration, the total content of hydrocarbon compounds having carbonnumbers of 10 or more (V (C₁₀₊)) on the bases of the whole fuel ispreferably 20 vol. % or less, more preferably 15 vol. % or less, furthermore preferably 10 vol. % or less, and most preferably 5 vol. % or less.

Incidentally, the above-described V (C₄), V (C₅), V (C₆), V (C₇+C₈), andV (C₁₀₊) are values quantitatively measured by the following gaschromatography. That is, these values are measured in conditions:employing capillary columns of methyl silicon for columns; using heliumor nitrogen as a carrier gas; employing a hydrogen ionization detector(FID) as a detector; the column length of 25 to 50 m; the carrier gasflow rate of 0.5 to 1.5 ml/min, the split ratio of (1:50) to (1:250);the injection inlet temperature of 150 to 250° C.; the initial columntemperature of −10 to 10° C.; the final column temperature of 150 to250° C., and the detector temperature of 150 to 250° C.

Further, the content of sulfur in a fuel of the invention is notparticularly restricted, however, because deterioration of a fuel cellsystem comprising such as a reforming catalyst, a water gas shiftreaction catalyst, a carbon monoxide removal catalyst, fuel cell stacks,and the like can be suppressed to low and the initial performances canbe maintained for a long duration, the content is preferably 50 ppm bymass or less, more preferably 30 ppm by mass or less, further morepreferably 10 ppm by mass or less, much further more preferably 1 ppm bymass or less, and most preferably 0.1 ppm by mass or less.

Here, sulfur means sulfur measured by JIS K 2541, “Crude Oil andPetroleum Products-Determination of sulfur content”, in case of 1 ppm bymass or more and means sulfur measured by ASTM D4045-96, “Standard TestMethod for Sulfur in Petroleum Products by Hydrogenolysis andRateometric Colorimetry” in the case of less than 1 ppm by mass.

In the invention, the respective contents of saturates, olefins andaromatics are not particularly restricted, however, the saturates (V(S)), olefins (V (O)) and aromatics (V (Ar)) are preferably 30 vol. % ormore, 35 vol. % or less, and 50 vol. % or less, respectively.Hereinafter, these compounds will separately be described.

In view of a high power generation quantity per weight, a high powergeneration quantity per CO₂ emission, a low fuel consumption of a fuelcell system as a whole, small THC in an exhaust gas, and a shortstarting time of the system, V (S) is preferably 30 vol. % or more, morepreferably 40 vol. % or more, further more preferably 50 vol. % or more,much further more preferably 60 vol. % or more, much further morepreferably 70 vol. % or more, much further more preferably 80 vol. % ormore, much further more preferably 90 vol. % or more, and mostpreferably 95 vol. % or more.

In view of a high power generation quantity per weight, a high powergeneration quantity per CO₂ emission, small deterioration of a reformingcatalyst to maintain the initial performances for a long duration, and agood storage stability, V (O) is preferably 35 vol. % or less, morepreferably 25 vol. % or less, further more preferably 20 vol. % or less,much further more preferably 15 vol. % or less, and most preferably 10vol. % or less.

In view of a high power generation quantity per weight, a high powergeneration quantity per CO₂ emission, a low fuel consumption of a fuelcell system as a whole, small THC in an exhaust gas, a short startingtime of the system, and small deterioration of a reforming catalyst tomaintain the initial performances for a long duration, V (Ar) ispreferably 50 vol. % or less, more preferably 45 vol. % or less, furthermore preferably 40 vol. % or less, much further more preferably 35 vol.% or less, much further more preferably 30 vol. % or less, much furthermore preferably 20 vol. % or less, much further more preferably 10 vol.% or less, and most preferably 5 vol. % or less.

Further, it is most preferable to satisfy the above-described preferableranges of sulfur and the above-described preferable ranges for thearomatics since deterioration of a reforming catalyst can be suppressedto low and the initial performances can be maintained for a longduration.

The values of the above-described V (S), V (O), and V (Ar) are allmeasured value according to the fluorescent indicator adsorption methodof JIS K 2536, “Liquid petroleum products-Testing method of components”.

Further, in the invention, the ratio of paraffins in saturates of a fuelis not particularly restricted, however, in view of a high H₂ generationquantity, a high power generation quantity per weight, a high powergeneration quantity per CO₂ emission and the like, the ratio ofparaffins in saturates is preferably 60 vol. % or more, more preferably65 vol. % or more, further more preferably 70 vol. % or more, muchfurther more preferably 80 vol. % or more, much further more preferably85 vol. % or more, much further more preferably 90 vol. % or more, andmost preferably 95 vol. % or more.

The above-described saturates and paraffins are values quantitativelymeasured by the following gas chromatography. That is, the values aremeasured in conditions: employing capillary columns of methyl siliconfor columns; using helium or nitrogen as a carrier gas; a hydrogenionization detector (FID) as a detector; the column length of 25 to 50m; the carrier gas flow rate of 0.5 to 1.5 ml/min, the split ratio of(1:50) to (1:250); the injection inlet temperature of 150 to 250° C.;the initial column temperature of −10 to 10° C.; the final columntemperature of 150 to 250° C., and the detector temperature of 150 to250° C.

Further, the ratio of branched paraffins in the above-describedparaffins is not particularly restricted, however, the ratio of branchedparaffins in the paraffins is preferably 30 vol. % or more, morepreferably 50 vol. % or more, and most preferably 70 vol. % or more inview of a high power generation quantity per weight, a high powergeneration quantity per CO₂ emission, a low fuel consumption of a fuelcell system as a whole, small THC in an exhaust gas, and a shortstarting time of the system.

The amounts of the above-described paraffins and branched paraffins arevalues quantitatively measured by the above-described gaschromatography.

Further, in the invention, the heat capacity of a fuel is notparticularly restricted, however, the heat capacity is preferably 2.6kJ/kg·° C. or less at 15° C. and 1 atm in liquid phase in view of a lowfuel consumption of a fuel cell system as a whole.

Further, in the invention, the heat of vaporization of a fuel is notparticularly restricted, the heat of vaporization is preferably 400kJ/kg or less because of a low fuel consumption of a fuel cell system asa whole.

Those heat capacity and heat of vaporization can be calculated from thecontents of respective components quantitatively measured by theabove-described gas chromatography and the numeric values per unitweight of the respective components disclosed in “Technical DataBook-Petroleum Refining”, Vol. 1, Chap. 1, General Data, Table 1C1.

Further, in the invention, the Reid vapor pressure (RVP) of a fuel isnot particularly restricted, however, it is preferably 10 kPa or more inrelation to the power generation quantity per weight and preferably lessthan 100 kPa in relation to suppression of the amount of an evaporativegas (evapo-emission). It is more preferably 20 kPa or more and less than90 kPa, further more preferably 40 kPa or more and less than 75 kPa, andmost preferably 40 kPa or more and less than 60 kPa. Here, the Reidvapor pressure (RVP) means the vapor pressure (Reid vapor pressure(RVP)) measured by JIS K 2258, “Testing Method for Vapor Pressure ofCrude Oil and Products (Reid Method)”.

Further, in the invention, the research octane number (RON, the octanenumber by research method) is not particularly restricted, however, itis preferably 101.0 or less since deterioration of a reforming catalystcan be suppressed to low and the initial performances of a reformingcatalyst can be maintained for a long duration owing to a high powergeneration quantity per weight, a low fuel consumption of a fuel cellsystem as a whole, small THC in an exhaust gas, and a short startingtime of the system. Here, the octane number by research method (RON)means the research method octane number measured by JIS K 2280,“Petroleum products-Fuels-Determination of octane number, cetane numberand calculation of cetane number index”.

Further, in the invention, the oxidation stability of a fuel is notparticularly restricted, however, it is preferably 240 minutes or longerin view of storage stability. Here, the oxidation stability is theoxidation stability measured according to JIS K 2287, “Testing Methodfor Oxidation Stability of Gasoline (Induction Period Method)”.

Further, in the invention, the density of a fuel is not particularlyrestricted, however, it is preferably 0.78 g/cm³ or less sincedeterioration of a reforming catalyst can be suppressed to low and theinitial performances of a reforming catalyst can be maintained for along duration owing to small THC in an exhaust gas and a short startingtime of the system. Here, the density means the density measuredaccording to JIS K 2249, “Crude petroleum and petroleumproducts-Determination of density and petroleum measurement tables basedon a reference temperature (15° C.)”.

A production method of the fuel of the invention is not particularlyrestricted. Practical method is, for example, the fuel can be preparedby blending one or more following hydrocarbon base materials; lightnaphtha obtained by the atmospheric distillation of crude oil, heavynaphtha obtained by the atmospheric distillation of crude oil,desulfurized full-range naphtha B obtained by desulfurization of naphthafraction obtained by distillation of crude oil, desulfurized lightnaphtha obtained by desulfurization of light naphtha, desulfurized heavynaphtha obtained by desulfurization of heavy naphtha, isomerate obtainedby converting light naphtha into isoparaffins by an isomerizationprocess, alkylate obtained by the addition reaction (alkylation) of lowmolecule weight olefins to hydrocarbons such as isobutane, desulfurizedalkylate obtained by desulfurizing alkylate, low sulfur alkylateproduced from desulfurized hydrocarbons such as isobutane anddesulfurized low molecule weight olefins, reformate obtained bycatalytic reforming, raffinate which is residue after extraction ofaromatics from distillate of reformate, light distillate of reformate,middle to heavy distillate of reformate, heavy distillate of reformate,cracked gasoline obtained by catalytic cracking or hydrocrackingprocess, light distillate of cracked gasoline, heavy diatillate-crackedgasoline, desulfurized cracked gasoline obtained by desulfurizingcracked gasoline, desulfurized light distillate of cracked gasolineobtained by desulfurizing light distillate of cracked gasoline,desulfurized heavy distillate of cracked gasoline obtained bydesulfurizing heavy distillate of cracked gasoline, a light distillateof “GTL (Gas to Liquids)” obtained by F-T (Fischer-Tropsch) synthesisafter cracking natural gas or the like to carbon monoxide and hydrogen,desulfurized LPG obtained by desulfurizing LPG, and the like. The fuelcan also be produced by desulfurizing by hydrotreating or adsorptionafter mixing one or more types of the above base materials.

Among them, preferable materials as the base materials for theproduction of the fuel of the invention are light naphtha, desulfurizedlight naphtha, isomerate, desulfurized alkylates obtained bydesulfurizing alkylates, low sulfur alkylates produced from desulfurizedhydrocarbons such as isobutane and desulfurized low molecule weightolefins, desulfurized light distillate of cracked gasoline obtained bydesulfurizing a light distillate of cracked gasoline, a light distillateof GTL, desulfurized LPG obtained by desulfurizing LPG, and the like.

A fuel for a fuel cell system of the invention may comprise additivessuch as dyes for identification, oxidation inhibitors for improvement ofoxidation stability, metal deactivators, corrosion inhibitors forcorrosion prevention, detergents for keeping cleanness of a fuel system,lubricity improvers for improvement of lubricating property and thelike.

However, since a reforming catalyst is to be scarcely deteriorated andthe initial performances are to be maintained for a long duration, theamount of dyes is preferably 10 ppm or less and more preferably 5 ppm orless. For the same reasons, the amount of oxidation inhibitors ispreferably 300 ppm or less, more preferably 200 ppm or less, furthermore preferably 100 ppm or less, and most preferably 10 ppm or less. Forthe same reasons, the amount of metal deactivators is preferably 50 ppmor less, more preferably 30 ppm or less, further more preferably 10 ppmor less, and most preferably 5 ppm or less. Further, similarly since areforming catalyst is to be scarcely deteriorated and the initialperformances are to be maintained for a long duration, the amount ofcorrosion inhibitors is preferably 50 ppm or less, more preferably 30ppm or less, further more preferably 10 ppm or less, and most preferably5 ppm or less. For the same reasons, the amount of detergents ispreferably 300 ppm or less, more preferably 200 ppm or less, and mostpreferably 100 ppm or less. For the same reasons, the amount oflubricity improvers is preferably 300 ppm or less, more preferably 200ppm or less, and most preferably 100 ppm or less.

A fuel of the invention is to be employed as a fuel for a fuel cellsystem. A fuel cell system mentioned herein comprises a reformer for afuel, a carbon monoxide conversion apparatus, fuel cells and the like,however, a fuel of the invention may be suitable for any fuel cellsystem.

The reformer is an apparatus for obtaining hydrogen, by reforming afuel. Practical examples of the reformer are:

(1) a steam reforming type reformer for obtaining products of mainlyhydrogen by treating a heated and vaporized fuel and steam with acatalyst such as copper, nickel, platinum, ruthenium and the like;

(2) a partial oxidation type reformer for obtaining products of mainlyhydrogen by treating a heated and vaporized fuel and air with or withouta catalyst such as copper, nickel, platinum, ruthenium and the like; and

(3) an auto thermal reforming type reformer for obtaining products ofmainly hydrogen by treating a heated and vaporized fuel, steam and air,which carries out the partial oxidation of (2) in the prior stage andcarries out the steam type reforming of (1) in the posterior stage whileusing the generated heat of the partial oxidation reaction with acatalyst such as copper, nickel, platinum, ruthenium and the like.

The carbon monoxide conversion apparatus is an apparatus for removingcarbon monoxide which is contained in a gas produced by theabove-described reformer and becomes a catalyst poison in a fuel celland practical examples thereof are:

(1) a water gas shift reactor for obtaining carbon dioxide and hydrogenas products from carbon monoxide and steam by reacting a reformed gasand steam in the presence of a catalyst of such as copper, nickel,platinum, ruthenium and the like; and

(2) a preferential oxidation reactor for converting carbon monoxide intocarbon dioxide by reacting a reformed gas and compressed air in thepresence of a catalyst of such as platinum, ruthenium and the like, andthese are used singly or jointly.

As a fuel cell, practical examples are a proton exchange membrane typefuel cell (PEFC), a phosphoric acid type fuel cell (PAFC), a moltencarbonate type fuel cell (MCFC), a solid oxide type fell cell (SOFC) andthe like.

Further, the above-described fuel cell system can be employed for anelectric automobile, a hybrid automobile comprising a conventionalengine and electric power, a portable power source, a dispersion typepower source, a power source for domestic use, a cogeneration system andthe like.

EXAMPLES

The properties of base materials employed for the respective fuels forexamples and comparative examples are shown in Table 1, Table 2, andTable 3.

Also, the properties of the respective fuels employed for examples andcomparative examples are shown in Table 4.

TABLE 1 desulfurized desulfurized full-range full-range light naphthanaphtha distillate of distillate of *1 B *2 reformate *3 reformate *4sulfur 0.3 0.3 0.5 0.2 hydrocarbon carbon number: C₄ vol. % 1.6 0.2 1.318.0 ratio carbon number: C₅ vol. % 12.5 9.5 9.1 49.9 carbon number: C₆vol. % 19.7 22.5 18.9 31.9 carbon number: C₇ vol. % 20.9 22.3 28.3 0.2carbon number: C₈ vol. % 24.3 24.4 32.2 0.0 carbon number: C₇ + C₈ vol.% 45.2 46.7 60.5 0.2 carbon number: C₉ vol. % 18.5 18.6 8.9 0.0 carbonnumber: C₁₀₊ vol. % 2.5 2.5 1.3 0.0 composition saturates vol. % 92.894.4 21.9 97.2 olefins vol. % 0.6 0.8 1.7 1.8 aromatics vol. % 6.6 4.876.4 1.1 paraffins in vol. % 85.5 87.3 98.1 99.0 saturates branched vol.% 44.4 45.0 63.7 62.9 paraffins in paraffins oxygen mass % 0.0 0.0 0.00.0 distillation initial boiling point ° C. 35.0 42.0 30.5 22.0 10%point ° C. 55.0 59.5 59.0 26.0 30% point ° C. 73.5 75.5 91.5 32.5 50%point ° C. 91.5 92.0 110.5 40.5 70% point ° C. 112.5 111.5 126.5 47.590% point ° C. 134.5 135.0 145.5 54.0 final boiling ° C. 155.5 152.5175.5 66.0 point heat capacity kJ/kg · 2.105 2.113 1.812 2.230 (liquid)° C. heat capacity kJ/kg · 1.523 1.536 1.218 1.586 (gas) ° C. heat ofkJ/kg 317.2 324.7 349.8 348.1 vaporization RVP kPa 66.9 58.6 62.5 127.5research octane 63.4 60.1 101.5 78.2 number oxidationmin. >1440 >1440 >1440 >1440 density g/cm³ 0.7085 0.7112 0.8055 0.6487net heat of kJ/kg 44225 44267 41509 44974 combustion middle to heavyheavy distillate of distillate of sulfolane reformate *5 reformate *6raffinate *7 sulfur 0.4 0.3 0.4 hydrocarbon carbon number: C₄ vol. % 0.00.0 0.7 ratio carbon number: C₅ vol. % 0.0 0.0 4.4 carbon number: C₆vol. % 0.6 0.0 46.2 carbon number: C₇ vol. % 36.2 0.0 47.6 carbonnumber: C₈ vol. % 47.9 0.0 1.1 carbon number: C₇ + C₈ vol. % 84.1 0.048.7 carbon number: C₉ vol. % 13.3 68.3 0.0 carbon number: C₁₀₊ vol. %2.0 31.7 0.0 composition saturates vol. % 4.5 0.4 95.5 olefins vol. %0.1 0.0 4.4 aromatics vol. % 95.4 99.6 0.1 paraffins in vol. % 98.4 97.498.2 saturates branched vol. % 48.4 86.8 72.5 paraffins in paraffinsoxygen mass % 0.0 0.0 0.0 distillation initial boiling point ° C. 102.5162.5 66.0 10% point ° C. 117.5 164.0 72.5 30% point ° C. 123.0 165.575.5 50% point ° C. 129.5 167.5 79.5 70% point ° C. 137.5 171.0 86.0 90%point ° C. 151.0 190.5 98.5 final boiling ° C. 191.5 270.0 126.0 pointheat capacity kJ/kg · 1.715 1.699 2.155 (liquid) ° C. heat capacitykJ/kg · 1.172 1.238 1.573 (gas) ° C. heat of kJ/kg 344.4 309.6 318.8vaporization RVP kPa 7.0 0.1 29.9 research octane 111.5 118.0 56.9number oxidation stability min. >1440 >1440 >1440 density g/cm³ 0.86210.8883 0.6821 net heat of kJ/kg 41024 41250 44585 combustion *1: thoseobtained by desulfurization of naphtha fractions obtained bydistillation of crude oil *2: those obtained by desulfurization ofnaphtha fractions obtained by distillation of crude oil *3: fractionsobtained by treating desulfurized heavy naphtha with a reforming process*4: light components obtained by further distilling reformate *5: middleto heavy components obtained by further distilling reformate *6: heavycomponents obtained by further distilling reformate *7: remainingfractions left after extracting aromatic from reformate with a sulfolaneprocess

TABLE 2 desul- desul- furized furized cracked cracked cracked crackedcracked light light heavy gasoline gasoline gasoline gasoline gasolinealkylate *8 *9 *10 *11 *12 *13 sulfur 80 1 7 0.7 110 8 hydrocarboncarbon number: C₄ vol. % 7.3 7.6 13.4 13.2 0.0 8.6 ratio carbon number:C₅ vol. % 25.1 25.3 47.1 47.0 0.2 3.2 carbon number: C₆ vol. % 20.1 20.329.2 29.9 7.2 2.8 carbon number: C₇ vol. % 18.1 18.2 8.8 8.7 23.5 2.5carbon number: C₈ vol. % 13.7 13.5 1.4 1.2 22.7 79.8 carbon number: C₇ +C₈ vol. % 31.8 31.7 10.2 9.9 46.2 82.3 carbon number: C₉ vol. % 11.411.1 0.0 0.0 21.3 1.1 carbon number: C₁₀₊ vol. % 4.3 4.0 0.0 0.0 25.12.0 composition saturates vol. % 47.2 53.3 45.0 46.5 33.0 99.8 olefinsvol. % 39.4 33.4 53.7 52.3 39.2 0.1 aromatics vol. % 13.4 13.3 1.3 1.227.8 0.1 paraffins in saturates vol. % 85.6 88.2 93.5 94.0 76.4 100.0branched paraffins in vol. % 88.6 88.3 86.1 86.3 88.5 91.3 paraffinsoxygen mass % 0.0 0.0 0.0 0.0 0.0 0.0 distillation initial boiling point° C. 31.5 30.5 24.5 24.5 108.0 31.0 10% point ° C. 51.5 50.5 32.5 31.0119.0 71.5 30% point ° C. 77.0 75.0 38.5 37.5 126.5 98.5 50% point ° C.111.5 108.0 45.0 44.5 135.0 105.5 70% point ° C. 150.5 145.0 53.5 53.5148.0 110.0 90% point ° C. 189.0 182.0 69.5 69.0 167.0 122.5 finalboiling point ° C. 216.5 199.0 93.5 92.0 183.5 181.5 heat capacity kJ/kg· 2.063 2.096 2.159 2.167 1.946 2.071 (liquid) ° C. heat capacity (gas)kJ/kg · 1.464 1.485 1.519 1.523 1.389 1.590 ° C. heat of vaporizationkJ/kg 333.2 330.5 353.2 352.7 311.2 289.8 RVP kPa 62.5 64.0 115.3 115.812.0 58.5 research octane 92.3 90.0 95.5 95.0 88.3 95.6 number oxidationstability min. 210 270 150 150 200 >1440 density G/cm³ 0.7388 0.73020.6601 0.6590 0.7798 0.6955 net heat of kJ/kg 43903 43827 44589 4455542949 44488 combustion *8: gasoline fractions obtained by treatingheavy, decreased pressure light oils and the like with a crackingprocess *9: gasoline fractions obtained by treating heavy, decreasedpressure light oils and the like with a cracking process and furtherdesulfurizing the resulting *10: light fractions obtained by distillingcracked gasoline *11: desulfurized light fractions obtained bydistilling cracked gasoline *12: heavy fractions obtained by distillingcracked gasoline *13: gasoline fractions obtained by treating butane,butene fractions with an alkylation apparatus

TABLE 3 low desul- desul- sulfur furized GTL furized alkylate alkylateisomerate naphtha LPG *14 *15 *16 *17 LPG *18 sulfur 0.1 0.5 0.3 0.1 20.4 hydrocarbon carbon number: C₄ vol. % 8.4 8.5 2.4 2.1 97.9 98.0 ratiocarbon number: C₅ vol. % 3.3 3.3 43.6 12.4 0.2 0.1 carbon number: C₆vol. % 2.9 2.9 53.6 19.7 0.0 0.0 carbon number: C₇ vol. % 2.4 2.5 0.321.0 0.0 0.0 carbon number: C₈ vol. % 80.2 79.9 0.1 23.6 0.0 0.0 carbonnumber: C₇ + C₈ vol. % 82.6 82.4 0.4 44.6 0.0 0.0 carbon number: C₉ vol.% 0.9 0.9 0.0 17.7 0.0 0.0 carbon number: C₁₀₊ vol. % 1.9 1.9 0.0 3.50.0 0.0 composition saturates vol. % 99.7 99.8 99.9 100.0 99.4 99.5olefins vol. % 0.2 0.1 0.1 0.0 0.6 0.5 aromatics vol. % 0.1 0.1 0.0 0.00.0 0.0 paraffins in saturates vol. % 100.0 100.0 98.4 100.0 100.0 100.0branched paraffins in vol. % 91.4 91.4 83.5 53.5 34.6 34.6 paraffinsoxygen mass % 0.0 0.0 0.0 0.0 0.0 0.0 distillation initial boiling point° C. 30.5 30.0 32.0 31.5 — — 10% point ° C. 71.0 71.0 40.5 47.5 — — 30%point ° C. 99.0 98.5 43.5 69.5 — — 50% point ° C. 105.0 106.0 46.5 92.5— — 70% point ° C. 110.5 111.0 51.0 113.5 — — 90% point ° C. 121.5 122.058.5 129.5 — — final boiling point ° C. 177.0 180.0 70.0 150.5 — — heatkJ/kg · 2.071 2.075 2.197 2.167 2.368 2.369 capacity ° C. (liquid) heatkJ/kg · 1.594 1.590 1.582 1.590 1.628 1.628 capacity ° C. (gas) heat ofkJ/kg 290.8 290.2 332.8 309.5 379.5 379.6 vaporization RVP kPa 59.5 59.091.0 72.3 338.0 339.0 research 95.4 95.4 81.8 51.5 95.0 95.0 octanenumber oxidation min. >1440 >1440 >1440 >1440 — — stability densityg/cm³ 0.6951 0.6954 0.6475 0.6825 0.5778 0.5776 net heat of kJ/kg 4450144480 44798 44576 45681 45689 combustion *14: gasoline fractionsobtained by treating desulfurized butane, butene fractions with analkylation process *15: substances obtained desulfurizing gasolinefractions obtained by treating butane, butene fractions with analkylation process *16: gasoline fractions obtained by treatingdesulfurized light naphtha with an isomerization process *17: “Gas toLiquid” naphtha fractions which are obtained by cracking natural gas orthe like to CO and H² and then subjecting to synthesis, decomposition,and isomerization *18: desulfurized LPG fractions

TABLE 4 Ex. Ex. Ex. Ex. 1 2 3 4 Mixing ratio LPG 2% 2% desulfurized LPGdesulfurized 100% full-range naphtha desulfurized full-range naphtha BGTL naphtha 100% isomerate 10% alkylate 10% 20% low sulfur alkylatedesulfurized alkylate sulfolane 10% raffinate cracked 40% light gasolinecracked 5% heavy gasoline cracked 40% gasoline desulfurized crackedlight gasoline desulfurized cracked gasoline distillate- 17% reformatelight 3% 4% distillate- reformate middle to 30% heavy distillate-reformate heavy 3% 4% distillate- reformate Properties Sulfur ppm by 0.30.1 39.0 4.0 mass ratio by carbon number carbon vol. % 1.6 2.1 6.8 9.8number: C₄ carbon vol. % 12.5 12.4 18.2 21.5 number: C₅ carbon vol. %19.7 19.7 22.8 13.7 number: C₆ carbon vol. % 20.9 21.0 18.3 14.9 number:C₇ carbon vol. % 24.3 23.6 20.2 30.9 number: C₈ carbon vol. % 45.2 44.638.5 45.8 number: C₇ + C₈ carbon vol. % 18.5 17.7 9.3 6.9 number: C₉carbon vol. % 2.5 3.5 4.3 2.3 number: C₁₀₊ Composition saturates vol. %92.8 100.0 58.7 45.2 olefins vol. % 0.6 0.0 18.5 21.6 aromatics vol. %6.6 0.0 22.8 33.2 paraffins in vol. % 85.5 100.0 94.0 97.3 saturatesbranched vol. % 44.4 53.5 80.5 83.0 paraffins in paraffins Density g/cm³0.7085 0.6825 0.7316 0.7348 Distillation properties initial ° C. 35.031.5 29.0 29.5 boiling point 10% point ° C. 55.0 47.5 43.5 48.0 30%point ° C. 73.5 69.5 66.5 70.5 50% point ° C. 91.5 92.5 89.0 93.0 70%point ° C. 112.5 113.5 116.0 109.0 90% point ° C. 134.5 129.5 153.0133.5 final ° C. 155.5 150.5 180.5 179.0 boiling point Reid vapor kPa 6772 73 73 pressure Research 63.4 51.5 90.1 99.7 octane number Oxidationmin. 1440 or more 1440 or more 760 960 stability Net heat of kJ/kg 4423044580 43560 43190 combustion Heat kJ/kg · 2.105 2.167 2.027 1.970capacity ° C. (liquid) Heat kJ/kg · 1.523 1.590 1.444 1.401 capacity °C. (gas) Heat of kJ/kg 317.2 309.5 329.9 336.2 vaporization Comp. Ex.Ex. Ex. Ex. 5 6 7 1 Mixing ratio LPG desulfurized 2% 2% LPG desulfurizedfull-range naphtha desulfurized 100% full-range naphtha B GTL naphthaisomerate 10% alkylate low sulfur 10% 20% alkylate desulfurized alkylatesulfolane 10% raffinate cracked light gasoline cracked heavy gasolinecracked gasoline desulfurized 40% cracked light gasoline desulfurized45% cracked gasoline distillate- 17% reformate light 3% 4% distillate-reformate middle to 30% 30% heavy distillate- reformate heavy 3% 4% 70%distillate- reformate Properties Sulfur ppm by 0.6 0.5 0.3 0.3 massratio by carbon number carbon vol. % 7.3 9.0 0.2 0.0 number: C₄ carbonvol. % 19.6 19.8 9.5 0.0 number: C₅ carbon vol. % 23.6 13.5 22.5 0.2number: C₆ carbon vol. % 18.0 16.0 22.3 10.9 number: C₇ carbon vol. %19.7 32.2 24.4 14.4 number: C₈ carbon vol.% 37.7 48.2 46.7 25.3 number:C₇ + C₈ carbon vol. % 8.6 7.3 18.6 51.8 number: C₉ carbon vol. % 3.2 2.32.5 22.8 number: C₁₀₊ Composition saturates vol. % 62.1 42.8 94.4 1.6olefins vol. % 15.8 21.1 0.8 0.0 aromatics vol. % 22.0 36.2 4.8 98.3paraffins in vol. % 94.7 97.3 87.3 98.2 saturates branched vol. % 80.984.6 45.0 54.8 paraffins in paraffins Density g/cm³ 0.7257 0.7406 0.71120.8804 Distillation properties initial ° C. 29.5 29.0 42.0 105.5 boilingpoint 10% point ° C. 42.0 47.5 59.5 123.0 30% point ° C. 66.0 70.0 75.5140.5 50% point ° C. 86.5 92.0 92.0 165.5 70% point ° C. 113.0 109.0111.5 178.5 90% point ° C. 146.5 133.0 135.0 192.5 final ° C. 179.0176.0 152.5 260.5 boiling point Reid vapor kPa 75 73 59 1 pressureResearch 90.8 99.8 60.1 110 octane or number more Oxidation min. 780 9801440 or more 1440 stability or more Net heat of kJ/kg 43580 43040 4426741180 combustion Heat kJ/kg · 2.048 1.957 2.113 1.704 capacity ° C.(liquid) Heat kJ/kg · 1.458 1.388 1.536 1.219 capacity ° C. (gas) Heatof kJ/kg 330.0 336.4 324.7 319.8 vaporization

These respective fuels were subjected to a fuel cell system evaluationtest, an evaporative gas test, and a storage stability test.

Fuel Cell System Evaluation Test

(1) Steam Reforming

A fuel and water were evaporated by electric heating and led to areformer filled with a noble metal type catalyst and kept at aprescribed temperature by an electric heater to generate a reformed gasenriched with hydrogen.

The temperature of the reformer was adjusted to be the minimumtemperature (the minimum temperature at which no THC was contained in areformed gas) at which reforming was completely carried out in aninitial stage of the test.

Together with steam, a reformed gas was led to a carbon monoxideconversion apparatus (a water gas shift reaction) to convert carbonmonoxide in the reformed gas to carbon dioxide and then the produced gaswas led to a solid polymer type fuel cell to carry out power generation.

A flow chart of a steam reforming type fuel cell system employed for theevaluation was illustrated in FIG. 1.

(2) Partial Oxidation

A fuel is evaporated by electric heating and together with air, theevaporated fuel was led to a reformer filled with a noble metal typecatalyst and kept at a 1100° C. by an electric heater to generate areformed gas enriched with hydrogen.

Together with steam, a reformed gas was led to a carbon monoxideconversion apparatus (a water gas shift reaction) to convert carbonmonoxide in the reformed gas to carbon dioxide and then the produced gaswas led to a solid polymer type fuel cell to carry out power generation.

A flow chart of a partial oxidation type fuel cell system employed forthe evaluation was illustrated in FIG. 2.

(3) Evaluation Method

The amounts of H₂, CO, CO₂ and THC in the reformed gas generated from areformer were measured immediately after starting of the evaluationtest. Similarly, the amounts of H₂, CO, CO₂ and THC in the reformed gasgenerated from a carbon monoxide conversion apparatus were measuredimmediately after starting of the evaluation test.

The power generation quantity, the fuel consumption, and the CO₂ amountemitted out of a fuel cell were measured immediately after starting ofthe evaluation test and 100 hours later from the starting.

The energy (preheating quantities) necessary to heat the respectivefuels to a prescribed reforming temperature were calculated from theheat capacities and the heat of vaporization.

Further, these measured values, calculated values and the heating valuesof respective fuels were employed for calculation of the performancedeterioration ratio of a reforming catalyst (the power generation amountafter 100 hours later from the starting divided by the power generationamount immediately after the starting), the thermal efficiency (thepower generation amount immediately after the starting divided by thenet heat of combustion of a fuel), and the preheating energy ratio(preheating energy divided by the power generation amount).

Evaporative Gas Test

A hose for filling a sample was attached to a fuel supply port of a 20liter portable gasoline can and the installation part was completelysealed. While an air venting valve of the can being opened, 5 liter ofeach fuel was loaded. On completion of the loading, the air ventingvalve was closed and the can was left still for 30 minutes. After thecan being kept still, an activated carbon adsorption apparatus wasattached to the air venting valve and the valve was opened. Immediately,10 liter of each fuel was supplied from the fuel supply port. After 5minutes of the fuel supply, while the air releasing valve being openedand kept as it was, the vapor was absorbed in the activated carbon andafter that, the weight increase of the activated carbon was measured.Incidentally, the test was carried out at a constant temperature of 25°C.

Storage Stability Test

A pressure resistant closed container was filled with each fuel andoxygen, heated to 100° C. and while the temperature being kept as itwas, the container was kept still for 24 hours. Evaluation was carriedout according to “Petroleum products—Motor gasoline and aviationfuels—Determination of washed existent gum” defined as JIS K 2261.

The respective measured values and the calculated values are shown inTable 5.

TABLE 5 Evaluation results EX. 1 EX. 2 EX. 3 EX. 4 Electric powergeneration by steam reforming method (reforming temperature = optimumreforming temperature 1)) Optimum ° C. 670 670 680 680 reformingtemperature Electric energy kJ/fuel kg initial performance 29850 3015029200 28860 100 hours later 29820 30130 28800 28780 performance 100hours later 0.10% 0.07% 1.37% 0.28% deterioration ratio Thermalefficiency 2) initial performance 68%  68%  67%  67%  CO₂ generationkg/fuel kg initial performance 3.098 3.074 3.151 3.178 Energy per CO₂KJ/CO₂-kg initial performance 9634 9808 9266 9081 Preheating energykJ/fuel kg 1341 1376 1309 1288 3) Preheating energy 4.5% 4.6% 4.5% 4.5%ratio 4) Electric power generation by partial oxidation reforming method(reforming temperature 1100° C.) Electric energy kJ/fuel kg initialperformance 14380 14810 13470 13000 100 hours later 14370 14800 1335012970 performance 100 hours later 0.07% 0.07% 0.89% 0.23% deteriorationratio Thermal efficiency 2) initial performance 33%  33%  31%  30%  CO₂generation kg/fuel kg initial performance 3.101 3.075 3.152 3.180 Energyper CO₂ KJ/CO₂-kg initial performance 4637 4816 4273 4088 Preheatingenergy kJ/fuel kg 1988 2056 1919 1874 3) Preheating energy 13.8% 13.9%14.2% 14.4% ratio 4) Evaporative gas test Evaporative gas g/test 7.5 7.86.1 8.1 Storage stability test Washed existent gum mg/100 ml 1 1 2 3Comp. EX. 5 EX. 6 EX. 7 Ex. 1 Electric power generation by steamreforming method (reforming temperature = optimum reforming temperature1)) Optimum ° C. 680 680 670 720 reforming Electric energy kJ/fuel kginitial performance 29300 28780 29840 26290 100 hours later 29150 2875029820 24910 performance 100 hours later 0.51% 0.10% 0.07% 5.25%deterioration ratio Thermal efficiency 2) initial performance 67%  67% 68%  64%  CO₂ generation kg/fuel kg initial performance 3.146 3.1853.099 3.294 Energy per CO₂ KJ/CO₂-kg initial performance 9313 9036 96317981 Preheating energy kJ/fuel kg 1310 1286 1359 1174 3) Preheatingenergy 4.5% 4.5% 4.6% 4.5% ratio 4) Electric power generation by partialoxidation reforming method (reforming temperature 1100° C.) Electricenergy kJ/fuel kg initial performance 13550 12880 14380 10540 100 hourslater 13500 12860 14370 10010 performance 100 hours later 0.37% 0.16%0.07% 5.03% deterioration ratio Thermal efficiency 2) initialperformance 31%  30%  33%  26%  CO₂ generation kg/fuel kg initialperformance 3.147 3.186 3.100 3.199 Energy per CO₂ KJ/CO₂-kg initialperformance 4306 4043 4639 3295 Preheating energy 3) kJ/fuel kg 19361866 1986 1637 Preheating energy 14.3% 14.5% 13.8% 15.5% ratio 4)Evaporative gas test Evaporative gas g/test 6.5 8.0 3.8 1.9 Storagestability test Washed existent gum mg/100 ml 2 1 1 2 1) the minimumtemperature at which no THC is contained in a reformed gas 2) electricenergy/net heat of combustion of fuel 3) energy necessary for heating afuel to a reforming temperature 4) preheating energy/electric energy

INDUSTRIAL APPLICABILITY

As described above, a fuel for a fuel cell system of the inventioncontaining hydrocarbon compounds with specific distillation propertieshas performances with small deterioration and can provide high output ofelectric energy and other than that, the fuel can satisfy a variety ofperformances for a fuel cell system.

1. A fuel for use in a fuel cell system, wherein said fuel hasdistillation properties; the initial boiling point in distillation of24° C. or higher and 50° C. or lower, the 10 vol. % distillationtemperature of 35° C. or higher and 70° C. or lower, the 90 vol. %distillation temperature of 100° C. or higher and 180° C. or lower, andthe final boiling point in distillation of 130° C. or higher and 210° C.or lower, a content of hydrocarbon compounds having 4 carbon atoms is 15vol. % or less, a content of hydrocarbon compounds having 5 carbon atomsis 5 vol. % or more, a content of hydrocarbon compounds having 6 carbonatoms is 10 vol. % or more, a content of hydrocarbon compounds having 7and 8 carbon atoms in total is 20 vol. % or more, and a content ofhydrocarbon compounds having 10 or more carbon atoms is 20 vol. % orless, a sulfur content is 1 ppm by mass or less, saturates are 30 vol. %or more, olefins are 35 vol. % or less, aromatics are 50 vol. % or less,a ratio of paraffins in saturates is 60 vol. % or more and a ratio ofbranched paraffins in paraffins is 30 vol. % or more.
 2. A fuel for afuel cell system according to claim 1, wherein a heat capacity of thefuel is 2.6 kJ/kg° C. or less at 15° C. and 1 atm in liquid phase and aheat of vaporization of the fuel is 400 kJ/kg or less.
 3. A fuel for afuel cell system according to claim 2, wherein a Reid vapor pressure ofthe fuel is 10 kPa or more and less than 100 kPa.
 4. A fuel for a fuelcell system according to claim 2, wherein a research octane number ofthe fuel is 101.0 or less.
 5. A fuel for a fuel cell system according toclaim 2, wherein an oxidation stability of the fuel is 240 minutes orlonger.
 6. A fuel for a fuel cell system according to claim 2, wherein adensity of the fuel is 0.78 g/cm³ or less.
 7. A fuel for a fuel cellsystem according to claim 3, wherein a research octane number of thefuel is 101.0 or less.
 8. A fuel for a fuel cell system according toclaim 3, wherein an oxidation stability of the fuel is 240 minutes orlonger.
 9. A fuel for a fuel cell system according to claim 3, wherein adensity of the fuel is 0.78 g/cm³ or less.
 10. A fuel for a fuel cellsystem according to claim 4, wherein an oxidation stability of the fuelis 240 minutes or longer.
 11. A fuel for a fuel cell system according toclaim 4, wherein a density of the fuel is 0.78 g/cm³ or less.
 12. A fuelfor a fuel cell system according to claim 5, wherein a density of thefuel is 0.78 g/cm³ or less.
 13. A fuel for a fuel cell system accordingto claim 7, wherein an oxidation stability of the fuel is 240 minutes orlonger.
 14. A fuel for a fuel cell system according to claim 7, whereina density of the fuel is 0.78 g/cm³ or less.
 15. A fuel for a fuel cellsystem according to claim 8, wherein a density of the fuel is 0.78 g/cm³or less.
 16. A fuel for a fuel cell system according to claim 10,wherein a density of the fuel is 0.78 g/cm³ or less.
 17. A fuel for afuel cell system according to claim 13, wherein a density of the fuel is0.78 g/cm³ or less.